The field of nanotechnology is exploding. The potential applications that exploit unique properties of common materials at the nanoscale are innumerable, and scientists are exploring these possibilities with increasing eagerness. Consequently, production of nanomaterials is outpacing the current understanding of their health effects. This study will help charaterize the toxicity of nanomaterials, so that the health of the public can be properly safeguarded against exposure to potentially harmful nanomaterials. The goal of this research is to address the uncertainty of nanomaterial toxicity by determining the effect of size, morphology, and surface charge on the bioavailability and toxicity of engineered nanomaterials while also revealing the cellular mechanisms that control their gastrointestinal uptake and intracellular processing. The specific aims of this study are: 1) determine the influence of particle size, shape, and surface change on the transepithelial transport eficiency, 2) determine the intracellular fate of engineered nanomaterials and the cellular response triggered by nanomaterial uptake, and 3) determine the influence of nanomaterial exposure on cell viability and the structural integrity of a mono-layer of epithelial cells. To acheive these aims, an in vitro gut model will be used to measure the transport efficiency of a library of nanomaterials ranging in size, morphology, and surface charge across a monolayer of epithelial cells, followed by real time tracking of single nanoparticles exposed to the same cell type and examination of exposed cell integrity by fluorescence microscopy. By applying these techniques systematically to nanomaterials of varying characteristics, a picture will emerge not only of which individual nanomaterials are more or less toxic, but also what properties are common to more and less toxic nanomaterials. With this knowledge, products and substances containing nanomaterials developed for applications involving widespread exposure to the population can be developed to minimize toxicity and the associated health risks. This applies directly to the goals of the National Toxicology Program of which the National Institute of Environmental Health Sciences of the National Institutes of Health is a core agency.